Method and system for providing high sensitivity giant magnetoresistive sensors

ABSTRACT

A method and system for providing a magnetoresistive sensor and a read head that includes the magnetoresistive sensor is disclosed. The method and system include providing a pinned layer, a nonmagnetic spacer layer and a composite sensor layer. The pinned layer has a first magnetization that is pinned in a particular direction. The nonmagnetic spacer layer resides between the composite sensor layer and the pinned layer. The composite sensor layer includes a CoFe layer and a composite layer adjacent to the CoFe layer. The composite layer includes CoFe and at least one of Ta, Hf, Ti, Nb, Zr, Au, Ag, Cu, B, C, O 2 , H 2  and N 2 .

FIELD OF THE INVENTION

The present invention relates to magnetic recording systems, and moreparticularly to a method and system for providing a high sensitivitygiant magnetoresistive sensor for high density recording applications.

BACKGROUND OF THE INVENTION

Currently in magnetic recording technology, magnetoresistive (MR)sensors are used in MR heads in order to read data from magnetic media.For higher density recording applications, the MR sensors are typicallygiant magnetoresistive (“GMR”) sensors, such as spin valves.

FIG. 1 depicts a conventional MR sensor 10 that is typically used forreading data from a recording media (not shown). The conventional MRsensor 10 typically resides in a conventional read head that isincorporated into a conventional merged head that includes theconventional read head as well as a conventional writer. Theconventional MR sensor 10 includes a conventional antiferromagnetic(AFM) layer 12, a conventional pinned layer 14, a conventionalnonmagnetic spacer layer 16, a conventional CoFe sensor layer 18 and aconventional capping layer 20. The conventional capping layer 20includes a conventional conductive layer 22 and a conventional cappinglayer.

The conventional pinned layer 14 and the conventional CoFe sensor layer18 are ferromagnetic. The magnetization of the conventional pinned layer14 is pinned in place by the conventional AFM layer 12. In certainconventional MR sensors (not shown) the conventional pinned layer 14 isa conventional synthetic pinned layer having two ferromagnetic layersthat are antiferromagnetically coupled (AFC) and separated by a Rulayer. The magnetization of the conventional CoFe sensor layer 18 isfree to rotate in response to an external magnetic field, such as onegenerated by the bits stored in a recording media. The conventionalnonmagnetic spacer layer 16 is a conductive material, such as copper. Inaddition, CoFe/Cu interface is preferably surfactant treated by exposingthe nonmagnetic spacer layer to oxygen. The conventional conductivelayer 22 is typically composed of copper. The purpose of treating thenonmagnetic spacer layer 16 is to adjust the interlayer coupling betweenthe conventional CoFe sensor layer 18 and the conventional pin layer 14and to reduce the magnetostriction of the conventional CoFe sensor layer18.

FIG. 2 depicts a conventional method 30 for fabricating the conventionalMR sensor. The conventional AFM layer 12 is provided, via step 32. Theconventional pinned layer 14 is then provided on the conventional AFMlayer 12, via step 34. The conventional nonmagnetic spacer layer 16 isthen fabricated, via step 36. The conventional CoFe sensor layer 18 isthen provided, via step 38. The conventional capping layer 20, includingthe conventional conductive layer 22 and the conventional capping layer24, are provided, via step 40.

Although the conventional MR sensor 10 formed using the conventionalmethod 30 functions, one of ordinary skill with readily realize that asthe thickness of the conventional CoFe sensor layer 18 is reduced,performance of the conventional MR sensor 10 degrades. For higherdensity recording applications, a sensor layer having a lowermagnetization and, therefore, higher sensitivity to small magneticfields is desired. As the thickness of the conventional CoFe sensorlayer 18 decreases to less than or equal to approximately twentyAngstroms (particularly less than fifteen Angstroms), the magneticproperties of the conventional CoFe sensor layer 18 degrade. Thecoercivity of the conventional CoFe sensor layer 18 increases. Inaddition, the anisotropy field (H_(k)) increases. Because theconventional CoFe sensor layer 18 no longer has soft magneticproperties, the magnetization of the conventional CoFe sensor layer 18does not readily change magnetic moment direction in response to anexternal field. In addition, the conventional CoFe sensor layer 18 mayhave very large magnetostriction. The dynamic range of the conventionalMR sensor 10 is reduced and it becomes difficult to control the biaspoint of the conventional MR sensor 10. Furthermore, the MR effectdecreases for thinner conventional CoFe sensor layers 18. Thus, thesignal from the conventional MR sensor 10 is reduced. As a result, aconventional MR sensor 10 may be unusable at lower thicknesses of theconventional CoFe sensor layer 18.

Accordingly, what is needed is a system and method for improving theability of MR sensors to function for higher density recordingapplications and, therefore, at smaller thicknesses of the sensor layer.The present invention addresses such a need.

SUMMARY OF THE INVENTION

The present invention provides a method and system for providing amagnetoresistive sensor and a read head that includes themagnetoresistive sensor. The method and system comprise providing apinned layer, a nonmagnetic spacer layer and a composite sensor layer.The pinned layer has a first magnetization that is pinned in aparticular direction. The nonmagnetic spacer layer resides between thecomposite sensor layer and the pinned layer. The composite sensor layerincludes a CoFe layer and a composite layer adjacent to the CoFe layer.The composite layer includes CoFe and at least one of Ta, Hf, Ti, Nb,Zr, Au, Ag, Cu, B, C, O₂, H₂ and N₂.

According to the system and method disclosed herein, the presentinvention provides a magnetoresistive sensor having improved performancefor smaller thicknesses of the CoFe layer in the composite sensor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a conventional magnetoresistive sensor.

FIG. 2 is a flow chart depicting a conventional method for providing aconventional magnetoresistive sensor.

FIG. 3A is a diagram of one embodiment of a magnetoresistive head inaccordance with the present invention.

FIG. 3B is a diagram of one embodiment of a magnetoresistive sensor inaccordance with the present invention.

FIGS. 4A and 4B are graphs depicting thermal stability of one embodimentof a magnetoresistive sensor in accordance with the present invention.

FIG. 5 is a flow chart depicting one embodiment of a method inaccordance with the present invention for providing a magnetoresistivehead.

FIG. 6 is a flow chart depicting one embodiment of a method inaccordance with the present invention for providing a magnetoresistivesensor.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an improvement in read heads. Thefollowing description is presented to enable one of ordinary skill inthe art to make and use the invention and is provided in the context ofa patent application and its requirements. Various modifications to thepreferred embodiment will be readily apparent to those skilled in theart and the generic principles herein may be applied to otherembodiments. Thus, the present invention is not intended to be limitedto the embodiment shown, but is to be accorded the widest scopeconsistent with the principles and features described herein.

Currently, MR heads are widely used in magnetic recording technology. Inconventional MR heads, a conventional MR sensor is used. Such aconventional MR sensor 10 is depicted in FIG. 1. The conventional MRsensor 10 includes a conventional sensor layer 18 that is composed ofCoFe. In addition, the current trend in magnetic recording technology istoward the use of thinner sensor layers 18 that can be used to detectlower signals from high-density recording media. However, one ofordinary skill in the art will readily realize that the performance ofthe conventional CoFe sensor layer 18, and thus the conventional MRsensor 10, dramatically degrades for low thicknesses of the conventionalCoFe sensor layer 18. Consequently, the conventional MR sensor 10 maynot function for high density recording applications.

The present invention provides a method and system for providing a readhead. The method and system comprise providing a shield, a read sensorand an insulating read gap disposed between the shield and the readsensor. In one aspect, the insulating read gap includes at least oneoxidized metal layer substantially free of pinholes. In another aspect,the insulating read gap includes at least one bilayer including a firstinsulating layer having a first insulator and a second insulating layerhaving a second insulator different from the first insulator.

The present invention will be described in terms of a particular readhead having certain components and particular materials. However, one ofordinary skill in the art will readily recognize that this method andsystem will operate effectively for other heads, other components andother materials. For example, the present invention is preferably usedin a merged head including a read head and a write head. In addition,the read head in which the present invention is used could include othersensors and other materials. The present invention is also described inthe context of certain methods having particular steps for providing theread sensor and head. However, one of ordinary skill in the art willreadily recognize that the present invention is consistent with the useof other methods having different and/or additional steps.

To more particularly illustrate the method and system in accordance withthe present invention, refer now to FIG. 3A, depicting one embodiment ofa read head 100 in accordance with the present invention. The read head100 is preferably incorporated into a merged head that includes the readhead 100 and a write head (not shown). The read head 100 is preferablybuilt upon a substrate 102 and includes a first shield 104, a first gap106, an MR sensor 120 in accordance with the present invention, a secondgap 108 and a second shield 110. The shields 104 and 110 are preferablyconductive and are used to shield the MR sensor 120 from the magneticfield generated by bits (not shown) which are not currently being read.The gaps 104 and 106 are preferably nonmagnetic insulators.

FIG. 3B is a diagram of one embodiment of a MR sensor 120 in accordancewith the present invention, as used in the MR head 100. The MR sensor120 includes an antiferromagnetic layer 121, a pinned layer 124, anonmagnetic spacer layer 126, a composite sensor layer 128 and a cappinglayer 134. The pinned layer 124 depicted is a synthetic pinned layerincluding ferromagnetic layers 122 and 125 separated by an AFC layer123. The AFC layer 123 is preferably nonmagnetic, conductive and has athickness that allows the magnetizations of the magnetic layers 122 and125 to be antiferromagnetically coupled. Note that although the pinnedlayer 124 is depicted as being a particular synthetic pinned layer,nothing the prevents the method and system from being used with a simpleor other pinned layer (not shown). The capping layer 134 preferablyincludes an oxygen containing copper conductive layer 136 and a TaOcapping layer 138. In addition, the nonmagnetic spacer layer 126 ispreferably composed of Cu. The CoFe/Cu interface between the sensorlayer 128 and the nonmagnetic spacer layer 126 is preferably treatedwith a surfactant by exposing the Cu spacer layer 126 to a trace amountof oxygen, as discussed below.

The composite sensor layer 128 includes two layers 130 and 132. Thefirst layer 130 is a CoFe layer 130. The second layer 132 is a compositelayer 132. The composite layer 132 includes a combination of Co andanother material. Thus, the composite layer 132 is a CoFeX layer. Xrepresents Ta, Hf, Ti, Nb, Zr, Au, Ag, Cu, B, C, O₂, H₂, N₂ or acombination of two or more thereof. In a preferred embodiment, thethickness of the CoFe layer 132 is less than or equal to twentyAngstroms. Because the CoFe layer can have the smaller, desiredthickness of between zero and twenty Angstroms, the CoFe layer 132 isused to sense the external magnetic field generated by a magneticrecording media (not shown). Also in a preferred embodiment, thethickness of the composite layer 134 is less than or equal to twentyAngstroms.

The composite layer 132 preferably has a higher resistivity than theCoFe layer 130, has a positive magnetostriction, lower magnetization andless effect of enhancing the MR ratio. The higher resistivity of thecomposite layer 134 ensures that less current passing through the MRsensor 120 is shunted away from the CoFe layer 130. In addition, thelower magnetization of the composite layer 132 the product of themagnetization and the layer thickness can be sustained while decreasingthe net moment of the composite sensor layer 128. Furthermore, the totalthickness of the composite sensor layer 128 (the thickness of the CoFelayer 130 and the composite layer 132) is larger, even though the netmoment of the composite sensor layer 128 is reduced. Consequently,sufficient room for spin dependent scattering to occur in the compositesensor layer 128 is provided. As a result, the magnetoresistance of thecomposite sensor layer 128 is enhanced. This enhancement is particularlynoticeable for lower thicknesses, such as less than fifteen Angstroms,of the CoFe layer 130. Because the composite layer 132 has a positivemagnetostriction, the magnetostriction of the CoFe layer 130 can becounteracted to a certain extent. In addition, the specific compositionof the composite layer 132, the element(s) chosen for X in the CoFe X,can be selected to improve the thermal stability and/or the reliabilityof the composite sensor 120. In addition, the anisotropy and coercivityof the composite sensor layer 128 are reduced over that of aconventional sensor layer including only CoFe.

Thus, using the composite sensor layer 128, including the CoFe layer 130and the composite layer 132, the magnetic properties of the compositesensor layer 128 do not substantially degrade, even at lower thicknessesof the composite sensor layer. The soft magnetic properties of thecomposite sensor layer 128 are thus retained even at lower thicknesses.As a result, the composite sensor layer 128 is capable of being usedwith high-density recording media, which generate a smaller externalfield. In addition, the magnetostriction of the MR sensor 120 isreduced. The MR sensor 120 can, therefore, be more easily biased.Furthermore, the magnetoresistance ratio of the MR sensor 120 remainshigh, even at lower thicknesses of the MR sensor 120.

For example, Table 1 depicts the resistivity and magnetic properties ofthe composite sensor layer 128. The quantities in Table 1 were measuredfor single films that are two hundred Angstroms in thickness. As can beseen in Table 1, the resistivity increases and the magnetizationdecreases when a composite layer 132 is introduced. Thus, as discussedabove, the composite layer 132 can reduce the net magnetization of thecomposite sensor layer 128 without substantially shunting current awayfrom the CoFe layer 130. The desired magnetization and resistivity canbe achieved by selecting the desired material(s) for X in the CoFeXcomposite layer 132.

TABLE 1 Magnetization CoFeX (atomic %) Structure Resistivity (μΩcm)(normalized) X = 0 fcc 17.57 1.00 X = Ti₁Cu₂ fcc 23.43 .91 X = B₅ fcc50.93 .82 X = Ta₅ fcc 115.56 .64

In addition, the magnetic properties of the sensor layer can beimproved. Table 2 depicts the magnetic properties of conventional MRsensors, such as the conventional MR sensor 10, as well as an MR sensor120 in accordance with the present invention. As can be seen in Table 2,the total resistance of the composite sensor layer 120 is reduced. Inaddition the magnetoresistance is improved in the composite sensor layer120 by increasing the layer thickness. In addition, the shunting ofcurrent to other layers, such as the capping layer 134, is reducedbecause of the larger resistivity of the composite layer 132. Inaddition, the use of the CoFeX composite layer 132 in proximity to thecapping layer 134 may be seen as stop layers for charge carriers thattravel to the conductive layer 136 and then top specular layers. Thus,the magnetoresistance ratio is improved. Furthermore, the response tothe small external magnetic fields and soft magnetic properties areimproved. In addition, the magnetostriction is also greatly reduced.Thus, performance of the composite MR sensor 120 is greatly improved.

TABLE 2 Sensor Layer Magneto- λ (thickness, in magnetic Rs ResistanceSens. Hint Hcf Hk (10⁻⁷ moment equivalence) (Ω/sq) (%) (%/Oe) (Oe) (Oe)(Oe) cm) CoFe(13) 21.2 13.7 1.13 2.73 3.77 8.44 −17.8 CoFe(11)/CoFeB(4)19.2 14.9 1.31 11.57 3.67 8.84 4.86 CoFe(11)/CoFeTiCu(4) 19.5 15.0 1.4012.85 2.77 7.53 −3.23 CoFe(11)/CoFeTa(4) 20.1 14.4 1.59 22.4 2.16 8.06−7.97 CoFe(11)/COFeN(4) 19.5 14.9 1.60 12.71 3.11 7.67 −3.50

In addition, the thermal stability of the composite MR sensor 120 isalso improved. FIGS. 4A and 4B are graphs 160 and 170 depicting thermalstability of one embodiment of a magnetoresistive sensor in accordancewith the present invention. The graph 160 depicts the variation of Rswith time for a conventional CoFe sensor layer 18 as well as a compositesensor 128 including a CoFe layer 130 and a CoFeX layer 132. Similarly,the graph 170 depicts the magnetoresistance ratio (ΔR/R) versus time fora conventional CoFe sensor layer 18 as well as a composite sensor 128including a CoFe layer 130 and a CoFeX layer 132. The sample for theconventional MR sensor 10 had the form:Si/Ta(20)/NiFeCr(50)/PtMn(150)/CoFe(20)/Ru(8.5)/CoFe(22)/Cu(18-22)/St/CoFe(13)/Cu(2-15)/TaO(10),where the numbers in parentheses are the thickness in Angstroms. Thesample for the MR sensor 120 having a composite sensor layer 128 has thethirteen Angstrom CoFe layer replaced by a composite sensor layer 128including a CoFe layer 130 and a CoFeX layer 132. As can be seen in thegraphs 160 and 170, there is less variation with temperature for thecomposite sensor 128 including a CoFe layer 130 and a CoFeX compositelayer 132. Thus, in addition to having improved magnetic properties, theMR sensor can be more thermally stable.

FIG. 5 is a high-level flow chart depicting one embodiment of a method200 in accordance with the present invention for providing a MR head.The method 200 is preferably used in fabricating the MR head 100. Thus,the method 200 is described in the context of the MR head 100 and the MRsensor 120 depicted in FIGS. 3A and 3B. A first shield 104 and a firstgap 106 are provided, via steps 202 and 204, respectively. The MR sensor120 having a composite sensor layer 128 is provided, via step 206. Step206 thus includes providing a CoFe layer 130 and a CoFeX layer 132, eachof which is preferably less than twenty Angstroms in thickness. Thesecond gap 108 is provided, via step 208. The second shield 110 is alsoprovided, via step 210.

FIG. 6 is a more detailed flow chart depicting one embodiment of amethod for performing step 206 in accordance with the present inventionfor providing a magnetoresistive sensor 120 having a composite sensorlayer. The method 206 is preferably used in fabricating the MR head 100.Thus, the method 206 is described in the context of the MR head 100 andthe MR sensor 120 depicted in FIGS. 3A and 3B. The AFM layer 122 isprovided, via step 220. In a preferred embodiment, the AFM layer 122 mayinclude PtMn. The pinned layer 124 is provided, via step 222. In apreferred embodiment, step 222 includes providing two ferromagneticlayers 122 and 125 separated by an AFC layer 123. The ferromagneticlayers 122 and 125 are antiferromagnetically coupled. Thus, step 222preferably provides a synthetic pinned layer. However, in an alternateembodiment, step 222 can be used to provide a simple or other pinnedlayer. The nonmagnetic spacer layer 126, which is preferably copper, isprovided, via step 224. Also in step 224, the copper spacer layer ispreferably treated by providing a trace of oxygen, preferably on theorder of 10⁻⁴ mT, after deposition so that the CoFe/Cu interfaces aretreated with a surfactant. The composite sensor layer 128 is provided,via step 226. Step 226 thus includes providing a CoFe layer 130 that ispreferably less than or equal to twenty Angstroms in thickness and aCoFeX layer 132 that is preferably less than twenty Angstroms inthickness. The capping layer 134 is then provided, via step 228. Step228 preferably includes providing the oxygen containing conductive layer136 and a TaO layer 138. The the conductive layer 136 preferablyincludes a copper layer that contains a trace of oxygen diffused intothrough a thin TaO top layer 138 after deposition. The TaO layer 138 isthen provided on the conductive layer 136.

Using the methods 200 and 206 a MR head 100 and MR sensor 120 having acomposite sensor layer 128 can be provided. The composite sensor layer128 includes a CoFe layer 130 and a CoFeX layer 132. Use of thecomposite sensor can improve the soft magnetic properties of the MRsensor 120, enhance the magnetoresistance ratio and improvemagnetostriction. Thus, performance of the MR sensor 120 and the MR head100 are improved.

A method and system has been disclosed for providing a read head havingan improved magnetoresistive sensor. Although the present invention hasbeen described in accordance with the embodiments shown, one of ordinaryskill in the art will readily recognize that there could be variationsto the embodiments and those variations would be within the spirit andscope of the present invention. Accordingly, many modifications may bemade by one of ordinary skill in the art without departing from thespirit and scope of the appended claims.

1. A magnetoresistive sensor comprising: a pinned layer having a firstmagnetization, the first magnetization being pinned in a particulardirection; a nonmagnetic spacer layer; and a composite sensor layer, thecomposite sensor layer having a CoFe layer and a composite layerimmediately adjacent to the CoFe layer, the composite layer includingCoFe and at least one of Ta, Hf, Ti, Nb, Zr, Au, Ag, Cu, B, C, O₂, H₂and N₂, the nonmagnetic spacer layer residing between the compositesensor layer and the pinned layer.
 2. The magnetoresistive sensor ofclaim 1 further comprising a magnetostriction control layer adjacent tothe composite sensor layer.
 3. The magnetoresistive sensor of claim 2wherein the magnetostriction control layer further includes an oxygencontaining layer of copper and a TaO layer.
 4. The magnetoresistivesensor of claim 1 further comprising: an antiferromagnetic layeradjacent to the pinned layer, the antiferromagnetic layer for pinningthe first magnetization of the pinned layer.
 5. The magnetoresistivesensor of claim 1 wherein the pinned layer is a synthetic pinned layer.6. The magnetoresistive sensor of claim 1 wherein the composite layerhas a thickness of no more than twenty Angstroms.
 7. Themagnetoresistive sensor of claim 1 wherein the CoFe layer is less thentwenty Angstroms in thickness.
 8. The magnetoresistive sensor of claim 1wherein the nonmagnetic spacer layer includes copper and wherein thenonmagnetic spacer layer is treated with oxygen.
 9. A read headcomprising: a shield; an insulating read gap; and a magnetoresistivesensor, the magnetoresistive sensor including a pinned layer, anonmagnetic spacer layer and a composite sensor layer, the pinned layerhaving a first magnetization that is pinned in a particular direction,the nonmagnetic spacer layer residing between the composite sensor layerand the pinned layer, the composite sensor layer having a CoFe layer anda composite layer immediately adjacent to the CoFe layer, the compositelayer including CoFe and at least one of Ta, Hf, Ti, Nb, Zr, Au, Ag, Cu,B, C, O₂, H₂ and N₂, the nonmagnetic spacer layer residing between thecomposite sensor layer and the pinned layer.
 10. A method for providingmagnetoresistive sensor comprising the steps: (a) providing a pinnedlayer having a first magnetization, the first magnetization being pinnedin a particular direction; (b) providing a nonmagnetic spacer layer; and(c) providing a composite sensor layer such that the nonmagnetic spacerlayer resides between the composite sensor layer and the pinned layer,the composite sensor layer having a CoFe layer and a composite layerimmediately adjacent to the CoFe layer, the composite layer includingCoFe and at least one of Ta, Hf, Ti, Nb, Zr, Au, Ag, Cu, B, C, O₂, H₂and N₂.
 11. The method of claim 10 further comprising the step of: (d)providing a magnetostriction control layer adjacent to the compositesensor layer.
 12. The method of claim 11 wherein the step of providingmagnetostriction control layer (d) further includes the step of: (d1)providing an oxygen containing layer of copper and a TaO layer.
 13. Themethod of claim 10 further comprising the step of: (d) providing anantiferromagnetic layer adjacent to the pinned layer, theantiferromagnetic layer for pinning the first magnetization of thepinned layer.
 14. The method of claim 10 wherein the pinned layerproviding step (a) further includes the step of: (al) providing asynthetic pinned layer.
 15. The method of claim 10 wherein the compositelayer has a thickness of no more than twenty Angstroms.
 16. The methodof claim 10 wherein the CoFe layer is less then twenty Angstroms inthickness.
 17. The method of claim 10 wherein the nonmagnetic spacerlayer includes copper and wherein the nonmagnetic spacer layer istreated with oxygen.
 18. A method for providing a read head comprisingthe steps: (a) providing a shield; (b) providing an insulating read gap;and (c) providing a magnetoresistive sensor, the magnetoresistive sensorincluding a pinned layer, a nonmagnetic spacer layer and a compositesensor layer, the pinned layer having a first magnetization that ispinned in a particular direction, the nonmagnetic spacer layer residingbetween the composite sensor layer and the pinned layer, the compositesensor layer having a CoFe layer and a composite layer immediatelyadjacent to the CoFe layer, the composite layer including CoFe and atleast one of Ta, Hf, Ti, Nb, Zr, Au, Ag, Cu, B, C, O₂, H₂ and N₂, thenonmagnetic spacer layer residing between the composite sensor layer andthe pinned layer.